Summary:
Importing `react` modules from `react-native` has been deprecated since 0.25 so I think it's safe to remove it now since everyone has migrated their code and it is now well know and documented that you import from different packages. This finishes the spring cleanup of `react-native-implementation.js` :)
**Test plan**
Tested that UIExplorer still works.
Closes#13354
Reviewed By: bvaughn
Differential Revision: D4928785
Pulled By: javache
fbshipit-source-id: 38c623c309b06b2cb5e73074833342d2745ab198